On 5/26/06, Tom Lane <tgl@xxxxxxxxxxxxx> wrote:
Well, this bears looking into, because I couldn't get anywhere near 20ms with mysql. I was using a dual Xeon 2.8GHz machine which ought to be
did you have a key on a,b,c? if I include unimportant unkeyed field d the query time drops from 70ms to ~ 1 second. mysql planner is tricky, it's full of special case optimizations... select count(*) from (select a,b,max(c) group by a,b) q; blows the high performance case as does putting the query in a view. mysql> select version(); +-----------+ | version() | +-----------+ | 5.0.16 | +-----------+ 1 row in set (0.00 sec) mysql> set global query_cache_size = 0; Query OK, 0 rows affected (0.00 sec) mysql> select user_id, acc_id, max(sample_date) from usage_samples group by 1,2 [...] +---------+--------+------------------+ 939 rows in set (0.07 sec) mysql> select user_id, acc_id, max(sample_date) from usage_samples group by 1,2 [...] +---------+--------+------------------+--------------+ 939 rows in set (1.39 sec) merlin
